The present invention relates to an actuator device comprising a flexible cable, which has one end connected to a controlled member, and a flexible sheath, inside which is mounted the flexible cable, in which at least one portion of the flexible cable consists of a shape-memory material, which is able to undergo a variation of shape following upon its heating, in order to control the controlled member.
Flexible-cable actuator devices find their application in a wide range of fields and in general wherever it is necessary to provide a mechanical transmission which is simple and inexpensive and will enable remote control of the displacement of a member. Flexible-cable actuator devices are, for example, used for providing manual-control actuations on motor vehicles, for example for release from inside of the rear hatchback or of the bonnet, or for actuation of mobile parts or of mechanisms of seats of motor vehicle, or for the actuation of mobile members of the engine or of facilities on board the motor vehicle. There is moreover known a wide range of applications also outside the automobile field.
A flexible-cable actuator device having the characteristics referred to at the start of the present description is known from the document DE-C-199 16 244. Said known device is designed to be controlled manually in all conditions of use. However, its actuation brings about an activation of the shape-memory element, with the consequence that the controlled member undergoes an additional displacement with respect to the one brought about by mere manual actuation.
In the prior Italian patent application No. TO2001A000618, filed on Jun. 27, 2001, and in the corresponding international patent application PCT/IB02/02361, the present applicant has proposed an actuator device comprising:
a flexible cable having one end connected to a controlled member, and
a flexible sheath inside which is mounted the flexible cable,
in which at least one portion of the flexible cable consists of a shape-memory material which is able to undergo a variation of shape following upon its heating in order to control the controlled member,
in which the aforesaid sheath is mounted with respect to a fixed supporting structure so as to be free to be displaced longitudinally only in a direction corresponding to the direction of actuation of the controlled member, and
in which, moreover, the aforesaid sheath is coupled to the controlled member so as to be able to transmit directly thereto a displacement in the aforesaid direction of actuation and to be, instead, uncoupled by the controlled member in the event of a movement in the opposite direction, in such a way that said actuator is able to be used both manually, as element of mechanical transmission, using the sheath as element of transmission, and exploiting the variation of shape of the shape-memory cable, which can be obtained with its heating. The heating can be obtained by causing passage of electric current through the shape-memory cable.
With the purpose of further improving the actuator device described above, the subject of the present invention is a device having all the characteristics referred to above and characterized in that said flexible cable is provided with a coating of elastomer or synthetic material moulded thereon and adherent thereto, which is elastically deformed when the shape-memory cable is activated, so as to favour return of the shape-memory cable to its resting position both thanks to its elastic return, and in so far as it accelerates cooling of the shape-memory cable after activation.
Preferably said coating is obtained by means of an operation of simultaneous extrusion (co-extrusion) together with the shape-memory cable.
It should be noted that the coating thus obtained adheres to the cable and constitutes a separate element both with respect to the sheath of the actuator device and with respect to possible further spacer coatings, which are also illustrated in the preceding patent application of the present applicant, set between the cable and the sheath.
The material of the coating co-extruded on the cable is chosen so as to enable a dual advantage to be obtained. On the one hand, said material is not an electrical conductor, so that it will not heat up, as, instead, the cable does heat up when the latter is traversed by electric current during activation of the actuator. Consequently, the material of the aforesaid co-extruded coating favours and accelerates the cooling of the shape-memory cable at the end of the activation step. A second important advantage lies in the fact that since the aforesaid coating is made of elastic material it acts as a distributed spring that undergoes a compressive stress when the cable made of shape-memory material is shortened following upon its activation. Consequently, the coating contributes to a rapid return of the cable into the resting condition, at the end of an activation step, not only in so far as it accelerates cooling, but also in so far as it pushes the cable towards its resting condition as a result of its elastic return.
Of course, the invention is of general application and can consequently be used also outside the automobile sector, and in particular in any sector where it may prove useful to apply an actuator device that can be actuated both manually and electrically. Shape-memory actuator elements have been known for some time and used in a wide range of fields in which it is necessary to have available actuator means of simple and low-cost structure. They use shape-memory metal alloys capable of being deformed following upon overstepping of a pre-determined transition temperature. In general, heating can be obtained by the actuator element detecting directly a variable temperature, or else by supply of an electric current through the actuator element so as to heat it by the Joule effect. In the case of the invention, the electrical-supply means can be associated to electronic-control means designed for controlling supply of electric current according to a signal detected by a temperature sensor, by a position or displacement sensor or by a potentiometer.
Of course, the configuration of the cable made of shape-memory material can be any whatsoever. In particular, the cable can also have a U-shaped configuration, with a forward stretch and a return stretch, and its two ends set adjacent to one another, or else again it is possible to provide a plurality of cables co-extruded inside one and the same coating material.